The present invention relates to signal processing and is particularly applicable but not limited to circuits for amplifying amplitude and phase modulated signals.
The communications revolution of the 1990""s has led to an increasing need for further and better means of transporting both data and voice communications. One offshoot of this revolution has been the burgeoning growth in wireless communications as more and more data is being transmitted by wireless means. For wireless handsets, wireless PDAs (personal digital assistants), and other wireless devices, one overarching concern is power consumptionxe2x80x94the less power a device consumes the more desirable it is. To this end, higher efficiency components, such as amplifiers, are desirable in these wireless devices.
One type of architecture which was used in the past but has fallen out of recent favor is the so called Chireix architecture. First suggested by Henry Chireix in 1935, the technique also known as xe2x80x9coutphasingxe2x80x9d involves separately phase modulating two signals and recombining them in a combiner or combining network. By judiciously adjusting the phase modulation of the two signals, the combined resulting signal can become amplitude modulated as well as phase modulated. This technique enables the use of saturated amplifiers or switching amplifiers for amplitude modulated signals.
Also called xe2x80x9campliphasexe2x80x9d by the RCA Corporation when used in some of their radio transmitters, the technique has recently fallen out of favor due to its seeming inapplicability when amplifying signals. Previous attempts used common forms of linear and saturating amplifiers such as Class A and Class AB amplifiers to try and amplify the two signals prior to their being combined. Unfortunately, these efforts have yielded unacceptable results as the resulting circuits were found to be insufficiently efficient. A Chireix based architecture, if properly working with sufficient efficiency, would offer advantages in not only power consumption but in other areas as well.
Based on the above, there is a need for, methods or circuits which overcome or at least mitigate the drawback of the prior art. Such a solution should provide the advantages of a Chireix or outphasing architecture while providing sufficient amplification efficiency to be useful.
The present invention provides circuits and methods for use in amplifying amplitude and phase modulated signals. A circuit uses a combiner with dual parallel signal amplifiers feeding it. The signal amplifiers have a low output impedance while the combiner does not provide any isolation between its inputs from the signal amplifiers. As in other Chireix architectures, the signals from the signal amplifiers are phase modulated prior to being fed to the combiner. The combiner then combines these two signals and, depending on how these two signals are phase modulated, the resulting output of the combiner is amplitude modulated as well as phase modulated. The signal amplifiers may be Class D or Class F amplifiers to provide high efficiency amplification of the signals.
In a first aspect, the present invention provides a circuit for providing amplification to signals, the circuit comprising:
a signal combiner;
at least two signal amplifiers each receiving and amplifying a signal, said signal amplifiers being coupled in parallel to said combiner, each of said signal amplifiers acting as a voltage source and having a low output impedance,
wherein
each signal received and amplified by each of said signal amplifiers is phase modulated;
outputs of each of said signal amplifiers are added by said combiner to produce a resulting signal; and
amplitude modulation and phase modulation of said resulting signal from said combiner is achieved by an addition of said outputs.
In a second aspect, the present invention provides a circuit for providing amplification to signals, the circuit comprising:
at least two signal amplifiers each receiving and amplifying a signal and each producing an amplifier output and acting as a voltage source; and
an signal combiner receiving each of said amplifier outputs in parallel, said signal combiner providing no isolation between said amplifier outputs,
wherein
each signal received and amplified by each of said signal amplifiers is phase modulated;
said amplifier outputs are added by said combiner to produce a resulting signal; and
amplitude modulation of said resulting signal from said combiner is achieved by an addition of said amplifier outputs.